This invention relates to a spark control system for an engine.
Conventional engine spark control systems generally include an ignition coil generating high potential pulses and a distributor which acts to distribute the high potential pulses to spark plungs sequentially.
Some advanced spark control systems generally called direct ignition systems do not have such a high potential distributor so that they are advantageous in maintenance free and reliability. In these systems, ignition coils are directly coupled to spark plungs respectively. These systems include a device to detect or discriminate which engine cylinder should be currently exposed to spark. In accordance with a signal from this cylinder discrimination device, the ignition coil corresponding to the cylinder needing spark is activated.
The cylinder discrimination device has a crank angle sensor including a signal disc rotatable together with the engine camshaft. In the case of a six-cylinder engine, the signal disc has angularly spaced six slits corresponding to the cylinders. As the signal disc rotates, the slits periodically unblock a fixed optical path. These periodical unblockages of the optical path is detected and converted into electrical pulses corresponding to the engine cylinders. One slit differs from others which are identical. This unique slit corresponds to a single reference cylinder and causes a particular pulse different from other pulses. the reference cylinder is discriminated by receiving a particular pulse. The other cylinders are discriminated by counting the pulses after the receipt of a particular pulse.
It is assumed that immediately after the unique slit passes the optical path, the signal disc stops as a result of halt of the engine. During re-start of this engine, it is difficult to discriminate the engine cylinders for an initial interval approximately corresponding to first two revolutions of the engine crankshaft.